Adrenergic mechanisms regulate many vital physiologic and biochemical events. Estradiol and progesterone have been shown to alter the contractile response of smooth muscle to adrenergic stimulation. In the human and rabbit a contractile response mediated by alpha adrenergic receptors is found when estrogens are dominant. When progesterone is present a beta receptor mediated relaxation occurs. The proposed studies will determine whether the change is caused by hormone induced changes in the population of alpha and beta receptors by studying the binding of 125 Iodohydroxybenzylpindolol, 3H-dihydroalprenolol, 3H-dihydroergocryptine and other adrenergic agonists and antagonists. The effects of estradiol and progesterone on the adrenergic receptors in other tissues including aorta, liver, pancreas and platelets will also be studied with these techniques to determine their role in the physiologic changes in cardiovascular function and carbohydrate metabolism in pregnancy and with hormonal contraception.